Process for preparing alpha, beta-unsaturated compounds



United States Patent Ofiice 3,351,76 Patented Jan. 2, 1968 3,361,786PROCESS FOR PREPARING u,,B-UNSATURATED COMPOUNDS Walter Fink, Zurich,Switzerland, assignor to Monsanto Company, St. Louis, Mo., a corporationof Delaware No Drawing. Filed Jan. 21, 1965, Ser. No. 427,166 4 Claims.(Cl. 260-4655) This application is a continuation-in-part of copendingapplication Ser. No. 127,816, filed July 31, 1961, now abandoned. Thepresent invention relates to a process for preparing c n-unsaturatedcompounds by splitting off a halogen acid with potassium fluoride fromcompounds which have at least one a-hydrogen atom and at least onefl-halogen atom to an activating group.

The compounds from which the u,,8-unsaturated compounds are 'made are ofthe general formula ACHRCXRR" wherein X is a halogen atom, preferably achlorine atom, R, R and R" are hydrogen, halo gen, or aliphatichydrocarbon radicals, preferably ali phatic hydrocarbon radicals havingnot more than 8 carbon atoms; and A is the COOH, a COOR", the -CN, the-CONH or the -CH=CH radical, where R' is usually a hydrocarbon radicalhaving not more than 22 carbon atoms and preferably an aliphatichydrocarbon radical.

A number of methods are known for dehydrohalogenation, especially forthe dehydrochlorination, starting from :,B-diChlO10 compounds. Thus, thedehydrohalogenation has been effected under conditions mentioned belowby the use of one of the following catalysts: in aqueous solutions orsuspension, acid agents like K SO H PO alkaline agents like NaOH, Na CONaHCO etc. (US. 2,245,547, US. 2,434,229 and Germ-an 1,078,100); sodiumacetate (US. 2,476,528); organic bases and amino acids (German 855,553and 883,891); dialkali-metal-, di-ammonium-, or alkali metal ammoniumphosphates or arsenates (British 723,547). In alcohol solutions, sodiumhydroxide (US. 1,864,884); sodium acetate (Angew. Chem, 60, 311 (-1948)).With the exclusion of water, sodium carbonate in a polar solvent(Belgium 574,233); carhoxylic acid amide, carboxylic acid nitrile orcarboxylic acid imide (German 1,021,357); primary, secondary or tertiaryamines (German 1,064,502). With the exclusion of water in the gaseousstate, aluminum oxide clay or carbon black at 200550 C., carboxylic acidamides, carboxylic acid nitriles or amines at 220-550 C. (German1,076,673).

Most of the enumerated methods have practical importance for thedehydrohalogenation of a, 8-dichloropropionic acid esters and -nitrilesand the given references are pertaining to such processes; however,these methods have one or several of the following disadvantages:hydrolysis of groups which may be present such as for example ester,amide, carboxylic acid halide, carboxylic acid anhydride, phosphorushalide, etc.; cleavage of metal organo bonds, bad yields,decarboxylation of unstable carboxylic acids, such as for exampleacetylene dicarboxylic acid; production of cycloaliphatic rings;isomerization; formation of alkoxy derivatives; use of expensivesolvents and catalysts, difiicult separation of reaction mixtures,discoloration of polymers manufactured thereof, need of polymerizationinhibitors.

The problem of producing earl-unsaturated compounds by a practicalprocess which is applicable to the production of compounds having avariety of structures has heretofore remained unsolved.

Now it has been found that halogen acid can be eliminated from compoundswhich possess in ii-position to a halogen atom an activating group A asdescribed above and a hydrogen atom a to this activating group A byreaction with potassium fluoride at relatively low temperatures,preferably in the absence of water. Furthermore, the organic catalystswhich have been used previously are expensive; whereas, the potassiumfluoride catalyst of the invention is relatively inexpensive and asurprisingly eflicient catalyst. Potassium fluoride as well as itsaddition product with hydrogen fluoride can easily be separated from thereaction mixture since these compounds are insoluble and non-volatileeven at high temperatures. The potassium fluoride catalyst is a verydurable catalyst and can be used and regenerated indefinitely. Apotassium fluoride catalyst causes no discoloration of the reactionproducts and of the polymers produced therefrom. At C., which is abouthalf of the commonly used reaction temperature, one obtains a yield ofpure wchloroacrylic acid ester (see Example 7 hereinbelow). It issurprising that in this new process the addition of a specialpolymerization inhibitor is not necessary even at temperatures up toabout C. because the salts which are present in the reaction mixtureapparently are very efiicient for this purpose. It has been reported inGerman Patent No. 952,803 that vinylsulfonic acid fluoride can beobtained by treating fi-chloroethanesulfonic acid or -chloride with KF;but the general application of this process has not been evident untilnow.

The process of the invention proceeds as follows:

wherein A, X, R, R and R" are as defined hereinabove.

A class of compounds which has considerable importance for carrying outthe new process, consists of easily available compounds possessing alsoin the a-position a halogen atom, especially a chlorine atom. Themanufacture of such dihalogeno compounds by adding halogen to thecorresponding c p-unsaturated cyano, carbonyl compounds, etc., or toconjugated dienes, etc. is well known. The most important of thesereactants or starting compounds for the process of the invention are OS-dichloropropionic acid,, a,/3-dichloropropionic acid esters,0:,fi-dlChlO1OPI0PiOI13IIlid6, a,fi-dichloropropi0nitrile and3,4-dichlorobutene-1. On the dehydrohalogenation of these compounds onehalogen atom remains and a-ChlO- roacrylic acid, a-chloroacrylic acidesters, a-chloroacrylamide, a-chloroacrylonitrile and2-chlorobutadiene-1,3, respectively are formed.

Carrying out the reaction the defined starting compounds are broughtinto intimate contact with at least twice the equivalent amount ofpotassium fluoride in a corrosion proof vessel. The reaction can becarried out with or without a solvent. In certain cases a solvent forpotassium fluoride may be favorable such as acetamide,N-methyl-acetamide, dimethylformamide, polyvalent alcohols, etc. Forcarrying out the reaction, temperatures in :the range from about 60-200C. are preferred. The reaction time is in the range of about 38 hours. Apolymerization inhibitor will normally not be necessary to temperaturesup to about 150 C. It is particularly desirable, if feasible, for theparticular reactant and product to separate continuously the unsaturatedproduct compound from the reaction mixture by distillation, preferablyunder reduced pressure. The KX and KP salts by-product can be separatedfrom the reaction mixture by filtration. The reaction products prior tofiltration containing the salts, can even be polymerized directlywithout salt removal and worked up into foils, which can be converted bylavage with water into more or less microporous foils according to thesalt content.

In Table 1 below is shown a comparison of the new dehydrohalogenationprocess of u,,8-dichloropropionic acid ester using KF and of some of theprocesses using other organic catalysts.

TABLE 1.DEHYDROCHLORINATION OF a,B-DICHLOROPROPIONIC ACID ESTER NumberAddition Time Conversion Parts Yield (hrs) (percent) (percent) Exam le9. 5 n-Butylpyrrolidine 6 78 70.9 (91) Examgle b 0.6 Phenothiazine 6 6766 (98. 5) Example 0 2 Quinoline 50 46 (92) Example 7 (herein) 7 100 100(100) Example 7 10 Example 18 100 g. of u,e-dich1oropropionic acid ethylester are strongly stirred with 68 g. of powdered potassium fluoride(molar ratio 1:2) at 80 C. for 7 hours. Then the a-chloroacrylic acidethyl ester which is formed is distiled ofi in vacuum. Yield: 78.7 g. ofcolorless liquid.

The fractionation shows that it consists of 100% pure a-chloroacrylicacid ester. If, for example, n-dodecyl A fraction with B.P. 86-87 C. iscontinuously distilled oil within 2 hours from the reaction mixturespecified in Example and using the same conditions.

Example 13-21 It is proceeded as mentioned in Example 20, thereby thereaction temperature and/ or time are varied. In three examplesphenothiazine as a polymerization inhibitor is used. The results areshown in the following Table 3.-

TABLE 3.DEHYDROCHLORINATION OF cz,fi-DICHLOROPROPIONITRILE No. (III)Temp, Time (IV) (III) Yield,

Parts 0. (hrs.) Parts Percent Addition Parts (percent) (0) back 100 1005 23. 7 33. 5 (95. 7) 100 100 5 14. 7 20. 8 (S5. 2) 100 120 5 47. 0 67.8 (98. 4) 100 120 5 27. 0 39. 2 (93. 2) 100 140 2 20. 7 28. 5 (92. 0)100 140 2 58. 4 83. 5 (92. O) 100 140 3 31. 2 43. 0 (95. 1) 100 140 555. 9 79. 0 ,(95. 8) 100 140 5 35. 0 40. 8 1 Phenothiazine 49. 5 (83. 1)

(III) 0:,fi-D ichloropropionitrile.

(IV) a-Ohloroacrylonitrile.

(0) In parentheses: Yield based on conversion.

Reaction product continuously distilled o1 u,;8-dichloropropionate oroxo-tridecyl a,fi-dichloropropionate is used in the method of Example 7rather than ethyl 0:,[3-diChlO1'OPI'OPiOI18tC, the resulting productsare n-dodecyl m-chloroacrylate and oxo-tridecyl u-chloroacrylate,respectively. A temperature in the range of about 7090 C. is especiallysuitable for carrying out the dehydrochlorination of thea,fi-dichloropropionates.

Examples l-JZ It is proceeded as indicated in Example 7, thereby thereaction temperature and/or time are varied. In three examples acetamideas a solvent and phenothiazine as a polymerization inhibitor are used.The temperatures mentioned are temperatures of reaction vessel. Theresults are shown in the following Table 2.

TABLE 2.-DEHYDROGHLORINATION OF a,B-DICHLOROPROPIONIC ACID ETHYL ESTERNo. (1) Parts Temp., C. Time, i (II) Parts (I) percent Addition PartsYield (0) (hrs.) back (percent) )=a,5-Dich1oropropi'onic acid ester.

)za-ChlOrOacryliC acid ester. ):In parentheses Yield based onconversion.

Example 20 wherein R and R" are selected from the class consisting ofhydrogen, chlorine and alkyl having not more than 8 carbon atoms,comprising reacting a compound of the formula CNCHCICCIRR wherein R andR" are as defined hereinabove, with at least twice the molar amount ofpotassium fluoride based on the compound CNCHClCClRR" at a sufiicientlyhigh temperature in the range of about;

50-200 C. to cause dehydrochlorination and for a time in the range ofabout 2 to 10 hours.

2. A process of claim 1 wherein reaction products formed arecontinuously distilled off from the reaction mixture.

3. A process of claim 1 wherein a polymerization inhibitor is added tothe reaction mixture.

6 4. A process of claim 1 wherein R and R" are hydrogen iatoms.

References Cited Nesmeyanov et aL: C.A., 42, 1948, pp. 4924-4925. Kitanoet al.: C.A., 50, 1956, p. 3995. Kit'ano et al.: C.A., 53, 1959, p.7969.

JOSEPH P. BRUST, Primary Examiner.

1. A PROCESS FOR PREPARING A,B-UNSATURATED COMPOUNDS OF THE FORMULA